1. Field of the Invention
This invention relates to a recording apparatus with a record head which is composed of a plurality of recording elements arranged in a line and which records two-dimensional image or other information on a recording medium, and to a recording method using the record head.
2. Description of the Related Art
An array head is a record head composed of a plurality of recording elements arranged in a line. Recording methods using an array head are, for example, of the following two types. A first method is to arrange in parallel with the main scanning direction an array head which has the same length as that of the main scanning range like a thermal head, transport a recording medium, such as recording paper, in the vertical scanning direction perpendicular to the main scanning direction with respect to the array head, thereby recording two-dimensional or other information on the recording medium.
A recording method using a thermal head has been disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2001-341429. Jpn. Pat. Appln. KOKAI Publication No. 2001-341429 has disclosed an initializing method and a rewriting method of obtaining good recorded images without residual images (uneven development) in rewriting the images on a reversible thermosensitive recording medium, and an apparatus for the methods. Jpn. Pat. Appln. KOKAI Publication No. 2001-341429 has described the operation of causing the thermal head to heat to the color developing temperature the entire surface or recording area of the reversible thermosensitive recording medium to be colored or decolored according to the difference in heating temperature or cooling speed after heating to color the entire surface or recording area, thereby uniformizing the recording layer.
A second method is to provide an array head composed of a plurality of recording elements arranged in a line in parallel with a direction in which a recording medium, such as a recording sheet, is transported, stop transporting the recording medium temporarily and cause the array head to scan in the main scanning direction perpendicular to the transporting direction of the recording medium to record a plurality of lines of image or other information on the recording medium at the same time, and then transport the recording medium over a distance corresponding to a plurality of lines and record a plurality of lines of image or other information on the recording medium repeatedly, thereby recording two-dimensional image or other information on the recording medium.
On the other hand, the following two methods of recording involve causing the laser beam output from a laser light source to scan in the main scanning direction. A third method is used in, for example, a laser printer. The third method is to apply to a polygon mirror 2 the laser beam output from a single laser light source 1, such as a semiconductor laser, as shown in FIG. 18, to cause the laser beam to scan in the main scanning direction A by the rotation or reciprocating movement of the polygon mirror 2 and at the same time, and transport, for example, a rewritable thermosensitive recording medium 3 capable of thermosensitive recording in the vertical scanning direction B, thereby recording two-dimensional image or other information on the thermosensitive recording medium 3.
A fourth method uses a semiconductor laser array 4 composed of a plurality of laser light sources arranged in a line as shown in FIG. 19. The fourth method is to cause the semiconductor laser array 4 to scan in the main scanning direction and at the same time, transport a thermosensitive recording medium 3 in the vertical scanning direction, thereby recording two-dimensional image or other information on the thermosensitive recording medium 3.
The thermosensitive recording medium 3 is a rewritable reversible medium which alternates between coloring and decoloring by specific temperature heating control and enables thermosensitive recording and thermosensitive erasing. FIG. 20 shows a coloring and erasing characteristic of the thermosensitive recording medium 3. When being heated to, for example, a melting point of 180° C. or higher, the thermosensitive recording medium 3 goes into a state where the dyes in the print layer and a developer are mixed with one another. Rapid cooling from this state causes the dyes and developer to be crystallized while they are mixed with one another, thereby producing colors. On the other hand, when the thermosensitive recording medium 3 is cooled slowly, the dyes and developer crystallize separately. As a result, the thermosensitive recording medium 3 cannot keep the colored state and goes into the erased state. Moreover, even at a temperature equal to or lower than the melting point of the dyes and developer, if the thermosensitive recording medium 3 is heated at this temperature for a specific period of time, the dyes and developer are separated from one another and crystallize, with the result that the thermosensitive recording medium 3 goes into the erased state. The erase temperature at this time is in the range of about 130° C. to 170° C. As described above, with the thermosensitive recording medium 3, information is printed and erased by controlling the temperature and time exactly.
However, in the first method, since the thermal head is brought into contact with the thermosensitive recording paper, the protective layer of the thermosensitive recording paper might be damaged.
In the second method, the transportation of the recording medium has to be stopped temporarily each time a plurality of lines of image or other information are recorded simultaneously onto the recording medium. Therefore, the second method is not suitable for high-speed recording.
In the third method using the single laser light source 1, as shown in FIG. 18, when the laser beam is caused to scan the thermosensitive recording medium 3 to record information, the power of the laser beam output from the laser light source 1 is so low that it takes time to heat the recording surface of the thermosensitive recording medium 3 to the color developing temperature and therefore the speed of recording to the thermosensitive recording medium 3 cannot be increased. It is conceivable that the speed of recording to the thermosensitive recording medium 3 is increased by using, for example, a high-power semiconductor laser as the laser light source 1. However, the beam diameter of the laser beam output from the high-power semiconductor laser cannot be narrowed down to a small value and therefore fine print dots cannot be formed on the thermosensitive recording medium 3. When a high-power gas laser is used, the apparatus is large in size and requires a large power supply capacity, which increases costs.
It is conceivable that a plurality of single semiconductor lasers are used and the individual laser beams output from the semiconductor lasers are superimposed on one another to increase the power of the laser beams. However, it is difficult to align the plurality of laser beams with one another to superimpose them. The number of laser beams which can be superimposed on one another is limited to 2 to 4. Superimposing more laser beams than this number increases the difficulty.
Like the fourth method, a method of using a semiconductor laser array 4 composed of a plurality of laser light sources arranged in a line can be considered. However, in the fourth method, when the main scanning range is set to, for example, a 4-inch width with 200 DPI, a semiconductor laser array 4 composed of 800 laser light sources arranged in a line is required, which naturally increases costs.
It is, accordingly, an object of the invention to provide a recording apparatus with a record head capable of realizing a high-speed recording operation without a significant increase in costs.